Electrical resistance element



April 14, 1953 w w, HOEL 2,635,161

ELECTRICAL RESISTANCE ELEMENT Filed May 8, 1951 INVENTOR. h e/vde 14 floe/ ATTOR NE Y6 Patented Apr. 14, 1953 ELECTRICAL RESISTANCE ELEMENT Wendell W. Hoel, Rockford; Ill., assignor to Barher-Colman Company, Rockford, 111., a corporation of Illinois Application May 8, 1951, Serial No. 225,080

8 Claims.

" This invention relates to electrical resistances of the type used in rheostats for engagement with a movable wiping contact and comprising a coil of wire helically wound around a supporting strip and having a low resistance contact beyond one end of the resistance coil.

The general object is to provide a resistance element of the above character which is easy to manufacture, which presents a contact surface of uniform contour throughout its length, and which may be bent readily to a desired arcuate shape.

A more detailed object is to form the low resistance contact as a separate helical coil abutting the end of the resistance coil.

The invention also resides in the novel manner of electrically connecting the adjacent ends of the two coils.

Other objects and advantages of the invention will become apparent from the following detailed description taken in connection with the accompanying drawings, in which Figure 1 is a perspective view of a rheostat having a resistance element embodying the novel features of the present invention.

Figs. 2 and 3 are plan views of the resistance element in the course of its manufacture.

Fig. 4 is a plan view of the finished element.

Figs. 5 and 6 are sections taken respectively along the lines 5-5 and 6-5 of Fig. 4.

In the form shown for purposes of illustration, the improved resistance element indicated generally at I0 is especially adapted for use in a rheostat l 1 comprising a body [2 around which the element I0 is bent and secured by terminal screws l3 with one edge of the element exposed for wiping engagement with a contact arm l4 fast on an actuating shaft 15 and swingable thereby between limit stops l 6 and IT.

The "element l0 comprises generally a thin and readily bendable strip of insulating material having a coil 18 of resistance wire Wound around one end portion and connected at one end to a terminal l9 and a conductor 20 of substantially lower unit resistance connected to the other coil end 21 and extending along the other end portion of the insulating strip 23 to a second terminal 22. Herein the terminals comprise flat clips fastened to the strip 23 by hollow rivets 24 projecting through holes 25 in the strip.

The coil l8 comprises a length of enameled resistance wire having one end portion 26 underlying the terminal clip is and clamped thereby against the strip 23. The wire extends through a hole 21 in the strip and then is coiled helically around the strip to form the resistance element l8, the adjacent convolutions being closely adjacent each other so that the resultant coil presents a substantially continuous edge surface for engagement with the wiper l4. Punched through the strip 23 at the end 2i of the coil 18 is a hole 28 through which the wire is threaded and then extended along the opposite side of the strip as indicated at 29. The insulation is removed from the full length of this portion of the wire [8. Finally, the extreme end 32 is threaded up through a hole 33 and drawn taut along the top surface of the strip 23.

The invention contemplates the iormationoi the conductor 20 of the resistance element from a wire, prefer-ably tinned copper, of substantially the same diameter as the resistance wire it wound around the strip into a coil 36 forming a continuation of the coil [8 so that the two coils l8 and 30 present a continuous relatively smooth surface for engagement by the wiper 14. To accomplish this, the length of the wire 20 needed to form the coil 30 of the desired length is pulled down through the hole 33, then along the underside of the strip and finally up through the hole 28 leaving a length 35 of wire on the under side of the strip alongside the wire 29 and also a loose end 36 on the .top of the strip adjacent the end 32. The winding is started at the hole 28 and continued helically around the strip and the two wires 29 and 35 in the same direction as the winding of the coil l8. Thus, the initial part 34 of the first convolution is alined with the end 2| of the coil l8. The coil 20 terminates at the hole 33 through which the loose end 37 is drawn upwardly and laid alongside of the ends 32 and 36. With all three ends drawn taut, they are covered by the clip 22 which is then riveted to the strip to clamp the wires n'rmly in place. The end 26 is similarly covered and clamped by the clip l9 against the strip 23.

The nnlshed resistance element is readily flexiblewithout changing its surface contour and may be bent around the insulating disk l2 and secured thereto by the screws. With the element thus mounted, an edge portion of each 0011 i8 and 30 is presented to the wiper. Thus the value of the resistance between the Wiper and the terminal 19 will be a minimum when the wiper is adjacent this terminal and increases progressively as the wiper is moved across the coil l8. Then as the Wiper passes beyond the inner end of the coil 18 and across the coil 30, the resistance value remains constant since the wire 34 is in firm con- 3 tact with the bared part 29 of the resistance wire at the inner end and all along the latter part.

It will be seen that the resistance element above described is very simple to manufacture with a minimum of soldering operations. The resistance and conductive portions of its surface are smooth and continuous and of uniform contour. The finished element may easily be bent to the contour of amounting. I claim as my invention:

1. A resistance element comprising a bendi-= able strip of insulating material, electrical terminals secured to opposed ends of said strip, a

resistance wire anchored to oneof said terminals; and coiled helically around and along one end portion of said strip beginning at said one terminal, the other substantially straight endportion of said wire being uncoiled and extended through a hole in said strip at the end -of'the coil and thence along a side of the strip to said other; terminal, and: a second wire of about the; same; diameter as but of different: conductivity than. said resistance wire, secured at opposite ends to; said second, terminal and havingsa substantially straight end portion extended along said; strip alongside said first straight portion andi-thencethrough said hole, the remainder of said second wire being coiled helically around saidistrip beginning atsaidhole andlextending along: the strip-toward said second terminal.

2 A resistance element comprising a bendable strip ofinsulating material, electrical terminals secured to opposed ends of said strip, a resistance wire: anchored to one of said terminals and coiled helically aroundand along one'end-portion oisaid strip beginning at said one terminal, the other. substantially straight end portion of said wirebeing uncoiled and: extended through ahole said strip atone endand coiled helically around,

nd, alon n nd 1201 91 01". sa d il -"1p, another end; portion of, said wire beinguncoiled andiex tended through a hole in said, strip at the end of the, coil and thence along aside of, the strip, and a second wire of .diiferent conductivity having one portion lying along said strip and extend;- ing through said hole, the remainder of said second'wire, being coiled helically around, said strip beginning at said hole and extending along the strip.

4; A resistance element comprising a bendable strip of insulating material, electrical terminals secured to opposed ends of said strip, a resistance wire anchored to one of'said terminals and coiled helically around and along one end portion of 4 said strip beginning at said one terminal, the other substantially straight end portion of said wire being uncoiled and extending along a side of the strip to said other terminal, and a second wire of about the same diameter as but of difierent conductivity than said resistance wire secured at opposite ends to said second terminal and having, one uncoiled portion extended along said strip, theremainder of said second wire being coiled helically around said strip and said uncoiled portions and extending along the strip toward, said second terminal.

5'. A resistance element comprising a bendable strip ofinsulating material, electrical terminals secured to; opposite; ends of said strip, a coil of resistance wire helically wound around one end portion of said strip and having its outer end secured to one of said terminals, and a similar coil; of different conductivity wire helically wound around the other end portion of said strip and having: its'outer end secured to said other; terminal, the adjacent endsof: said coilsabuttingeach other and the corresponding-endsroi said,- two wires being extended througlrsaidstrip-and thence along the latter within, said second: coil.

6. A resistance element comprising astrip of:

insulating material, a coil ofresistanoe ,wire-helically Wound around oneend portionv of said, strip, and av coilof higher conductivity wire; helically wound around the, opposite end portion of said strip in abutment with thefirst coilgso, that the two coils present a continuous surface.

of uniform contour, the adjacent: ends of the two wires being extended. into and. surrounded by one of said coils.

7. A resistance element; comprising a, strip; of

insulating material, a coil of resistance wire helically wound around one end portion -,of said1strip-.

and a coil of diiferent conductivitywire, helicmly wound around the opposite end, portion ofsaid strip in abutment with the-first coilso that the: two coils present a continuous surfaceof. uniform-- contour, the inner end of saidfirst wire being extended througha hole in said stripandthence outwardly within the second, coil. and. along said.-

strip.

8. A resistance element comprising; a strip, of;

strip in abutment-with the first-coilso, that the: two coils,present, acontinuous surface ofuniform contour, the inner end ofsaid firstl wire,- y extending at least partially through said, second coil and electrically; connected to the convclu tions thereof;

WENDELL W-.. HOEL.

References Cited in the file of this patent; UNITED STATES .PA'IENTS-i- Number Name Date 1,755,314 Carter- Apr; 22, 1930 2,468,144 Van Alen Apr; 2611949 

